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Migrating Applications to the Cloud: Rehost, Refactor, Revise, Rebuild, or Replace?
3 December 2010
 
Richard Watson  

The CIO issues a simple directive: "Move some applications to the cloud." To do this, architects face bewildering choices. In this Decision Point, Principal Research Analyst Richard Watson steers architects to a choice from among five alternatives: Rehost on HIaaS, refactor using SIaaS and PaaS, revise for HIaaS or PaaS, rebuild on PaaS, or replace with SaaS. The decision must consider an organization's requirements, evaluation criteria, and architecture principles. However, no alternative offers a silver bullet: All alternatives require architects to understand application migration from multiple perspectives and criteria, such as IT staff skills, existing investments, and application architecture.





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Table of Contents

Contents
  • Decision Point
  • Decision Context
    • Business Scenario
    • Architectural Context
    • Related Decisions
  • Evaluation Criteria
    • Requirements and Constraints
      • Migration Goals and Priorities
      • Legacy Application Characteristics
      • Modernization Requirements
      • Application Platform and Architecture Principles
      • Development and Operations Skills Constraints
      • Migration Cost Considerations
    • Principles
  • Alternatives
    • Rehost
    • Refactor
    • Revise
    • Rebuild
    • Replace
    • Comparing Alternatives
    • Distinguishing Products from Services
  • Future Developments
    • Progress on Portability Standards
    • Evolution of Cloud Business Models
    • Incumbent Platform Players Will Wake Up
  • Decision Tool
    • Pre-Decision Assumptions
      • Assumption 1: Quality of Service Risks
      • Assumption 2: IT Portfolio Management Frameworks
    • Using the Decision Tools
      • Decision Filters
      • Migration Goals Assessment Tool
  • Decision Justification
    • Use Rehost
    • Use Refactor
    • Use Revise
    • Use Rebuild
    • Use Replace
  • Recommended Reading
  • Revision History
  • Notes
Tables
Table 1.
Gartner Frameworks to Apply Before This Cloud Migration Decision Point
Table 2.
Defining the Rehost Migration Option
Table 3.
Defining the Refactor Migration Option
Table 4.
Defining the Revise Migration Option
Table 5.
Defining the Rebuild Migration Option
Table 6.
Defining the Replace Migration Option
Table 7.
Which Elements of the Migrated Application Change, Need to Be Updated, or Entirely Replaced with Each Alternative?
Table 8.
Distinguishing Cloud Services from Enabling Products
Figures
Figure 1.
IT Portfolio Management Programs Giving This Decision Point Context
Figure 2.
Legacy Modernization Options Mapped to Cloud Migration Alternatives
Figure 3.
Relating This Decision Point to the Steps of Gartner's IT1 Cloud Adoption Strategy Guidance Framework
Figure 4.
The Rehost, Refactor, Revise, Rebuild, and Replace Cloud Migration Alternatives Mapped to the Four Cloud Tiers (HIaaS, SIaaS, PaaS, and SaaS) and Examples of Cloud Service Providers
Figure 5.
Steps Required to Use the Cloud Migration Decision Tools
Figure 6.
Conditions for Filtering out the Rehost Migration Alternative
Figure 7.
Conditions for Filtering out the Refactor and Revise Migration Alternatives
Figure 8.
Conditions for Filtering out the Rebuild Migration Alternative
Figure 9.
Conditions for Filtering out the Replace Migration Alternative




Document History:
 
Decision Point for Selecting an Application's Cloud Migration Strategy
3 July 2012
  
Migrating Applications to the Cloud: Rehost, Refactor, Revise, Rebuild, or Replace?
3 December 2010
  




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